A Model for Using Qualitative Variables as Covariates in the Analysis of Covariance. Technical Paper 266.

Ross, N. Phillip

The U.S. Army Research Institute for the Behavioral and Social Sciences has developed a wide range of statistical models to test hypotheses generated in relation to an equally wide range of measurement and evaluation situations. The randomized block (RB) design has traditionally been a preferred model for much psychological research. The RB has had, however, the stringent requirement that the sample population be strictly defined and stratified beforehand, a requirement more appropriate in a controlled laboratory environment than in many field situations. This technical paper describes the development of an alternative statistical design which provides the advantages of the classic RB method without its operational disadvantages, and which will be useful not only in the area for which it was developed, but in other areas of behavioral science research. The statistical model chosen for comparison and test was a modified analysis of variance (ANCOVA) design that does not require previously selected stratified samples and does incorporate the ability to handle categorical variables: the categorical analysis of covariance (CANCOVA). Empirically, no practical difference was found between the power of RB and CANCOVA when the samples were large. (Author/NG)